THE SKELETON 433. 
(c) in the orbital region: the basisphenoid, the orbitosphenoids, 
the alisphenoids and ossifications of the interorbital septum; (d) in 
the ethmoidal region the bony ethmoidal skeleton; (e) the palato- 
quadrate cartilage furnishes the quadrate bone; (/) a proximal 
ossification, the articulare, arises in Meckel’s cartilage and fuses 
later with membrane bones; (g) the upper part of the hyoid arch 
furnishes the columella, and the ceratohyals the os entoglossum; 
(h) the cerato- and epibranchials ossify independently, as also 
do the two copule. (See Figs. 243, 244 and 245.) 
The membrane bones of the skull are: (a) in the region of the 
cranium proper: parietals, frontals, squamosals; (6) in the facial 
region: lachrymals, nasals, premaxille, manille, jJugals, quad- 
rato-jugals, pterygoids, palatines, parasphenoid, and vomer; (c) 
surrounding Meckel’s cartilage and forming the lower Jaw: angu- ¢ 
lare, supra-angulare, operculare, and dentale. (See Figs. 243, 244 
and 245.) 
The embryonic bird’s skull is characterized by a wealth of 
distinct bones that is absolutely reptilian; but in the course of 
development these fuse together so completely that it is only in 
the facial and visceral regions that the sutures can be distinguished 
readily. 
In order of development the membrane bones precede the 
cartilage bones, though the latter are phylogenetically the older. 
Thus, about the end of the ninth day, the following bones are 
present in the form of delicate reticulated bars and plates: all 
four bones of the mandible, the faint outline of the premaxille, 
the central part of the maxilla, the jugal and quadratojugal, the 
nasals, the palatines and pterygoids. The base of the squamosal 
is also indicated by a small triangular plate ending superiorly in 
branching trabecule, delicate as frost-work. A faint band of 
perichondral bone is beginning to appear around the otic process 
of the quadrate, the first of the cartilage bones to show any 
trace of ossification. These ossifications. appear practically 
simultaneously as shown by the examination of the earlier stages. 
On the twelfth day these areas have expanded considerably, 
and the frontals and prefrontals (lachrymals) are formed; the 
rostrum of the parasphenoid is also laid down, and the exoccipi- 
tals appear in the cartilage at the sides of the foramen magnum. 
The parietals appear behind the squamosal (Fig. 242) about the 
thirteenth day; the basioccipitals soon after. The supraoc- 
